218 



ELEMENTS OF PHYSIOLOGY 



pancreatic juice, is alkaline, and contains three ferments, 

 one of which (amylopsin) is hardly to be distinguished 

 from the ptyalin of the saliva, and continues the. digestion 

 of the starchy food ; another (trypsin) has an action 

 similar to pepsin, and digests proteids ; while the third 

 (steapsin) begins the digestion of an important class of 



foods, the fats, which have not 

 heretofore come in contact with 

 a digestive fluid that could act 

 upon anything more than the 

 proteid envelopes of the fat cells 

 (see Plates). 



388. Digestion of Fats. Fats 

 are digested not by going into 

 solution, but by the large globules 

 of fat being broken into very 



FIG. 173. Semi-diagrammatic minute globules. Such globules, 



View of Two Villi of the Small . . .. ., . , . 



intestine. Magnified about floating in a liquid, form what is 



50 diameters. called an emulsion. Milk is an 



a> substance of the viiius; t, its epi- emulsion of cream. It is the 



thelium; c, a, the artery and vein, 



with their connecting capillary net- Cream in SWCCt milk which glVCS 



work which envelopes and hides f, , .-\ > . r i 



the lacteal that occupies the C en- it the white appearance, for the 



ter of the villus and opens into a g^buleS of fat reflectthe light, 

 network of lacteal vessels at the base. j 



When it is churned these minute 



particles touch and adhere, forming butter. Fats are not 

 acted on by acids, but they are acted upon by alkaline 

 fluids. The steapsin ferment from the pancreas, aided by 

 the alkaline bile from the liver, emulsifies the fats, and pre- 

 pares them for absorption. 



389. Absorption of the Fats. The fats are absorbed by 

 the lymphatic system. Many minute lymphatics called 

 lacteals (Fig. 173) are found in the villi of the intestines, 

 and the epithelial cells of the mucous lining take up the 

 fat and transmit it, slightly changed, to these lacteals, 

 which unite one to another and empty into the thoracic 



